Generally, three factors contribute to engine oil contamination: by-products given off by combustion, debris entering through an engine's air intake, and metal shavings created by engine wear. In particular, these metal shavings (on the order of 100 microns or less) are indicative of the health of the machine. The physical characteristics (e.g., size and shape) of these metal shavings and other observed debris may contain information relating to the real-time health of the machine.
In today's marketplace, automotive manufacturers have developed numerous systems for inferring whether a user needs to change engine oil or other automotive fluids. An example of such a system is an onboard monitoring system in most automobiles that tracks several variables including engine running time, vehicle mileage, and temperature. Based on this information, an onboard computer calculates when the engine oil should be changed and, in turn, lights the oil lamp indicator on the vehicle's dashboard. While this and other similar systems may notify automobile owners of oil change deadlines, these systems lack the capacity to directly detect if metal shavings or other contaminants exist in the engine oil and are unable to determine the real-time health of the machine.
In light of this shortcoming, systems that directly analyze fluid were developed. The traditional method for directly analyzing a fluid was to extract an oil sample from a disengaged engine, and then to send the oil to a laboratory for testing. Although necessary for safety, this process was time consuming.
More recently, systems utilizing optical near-field imaging techniques have been developed. These systems generally consist of a light source, a light detection device, a flow cell, and a pump or other means to deliver the fluid to the flow cell. One such system, the optical near-field imaging system disclosed in U.S. Pat. No. 6,104,483, incorporated herein by reference, determines the number of particles in the fluid, then tabulates each particle's size and physical characteristics. The physical characteristics of a particle directly correspond to a particular wear mechanism. Thus, in undergoing an analysis of engine oil, this system can correlate the tabulated information with a specific wear mechanism (e.g., metal shavings created by engine wear or debris entering through an engine's intake). Ultimately, the system could inform a user to the source of the particles, thereby enabling the user to diagnose and remedy any problems that may exist.
While these optical near-field imaging systems show promise in making real-time diagnoses of machines, current systems have a major shortcoming, namely, they cannot withstand the stresses associated with the high pressures or high temperatures present in an engine or similar environment. In this type of environment, pressures may routinely reach 5000 psi and temperatures may reach 140° C. Accordingly, systems utilizing optical near-field imaging techniques have not been successfully incorporated into these environments.
While known flow cells are sufficient in their stated purpose, these devices are not built to withstand the high pressure and high temperatures that exist when a device is mounted directly in an engine or similar environment. Therefore, the need exists for a flow cell that can withstand high pressures and high temperatures, while still obtaining accurate measurements and images.